Infestation of gold-spotted oak borers are ravaging trees that form crucial habitat for many creatures

In a secluded spot of William Heise County Park is a graveyard of oak trunks — a final resting place for hundreds of trees felled by an infestation that’s harming forests across the San Diego region.

Piles of oak logs, some several feet in diameter, lie chopped in sections. Outside the graveyard, the loss of those trees is evident throughout the park, with stark new clearings scarred by thick stumps.

The oaks were casualties of the gold-spotted oak borer, an exotic beetle that hitchhiked into California on firewood more than a decade ago and has since ravaged centuries-old trees throughout the backcountry.

A few years ago, the pest cropped up in Marian Bear Memorial Park near La Jolla. Then late last year, it showed up for the first time in Idyllwild, a rustic town in the San Jacinto Mountains of Riverside County.

Scientists said the beetle’s effect is devastating because oaks, the only native Southern California trees capable of producing dense canopies, are crucial habitat for many creatures.

“They’re really the linchpin of an awful lot of ecosystems, and it’s sort of sickening to see how many trees have died and how many are in trouble,” said Tom Scott, a natural resource specialist for the University of California. “It’s one of the most dramatic changes we’ve seen to oak woodlands.”

Researchers have spent years trying to determine if the oak borer has a natural predator. They warn against transporting firewood to other regions, because that could expand the beetle’s path of destruction. And they have deployed a network of volunteers to watch for new oak-borer hot spots.

One of those volunteers, retired Cal Fire employee Mark Ostrander, said he logs 20 to 30 hours per week checking oaks in his neighborhood of Jacumba.

“What if San Diego County had no oaks in it?” Ostrander said. “What do you think the landscape would look like? What would the parks be like?”

William Heise County Park, near Julian, offers a glimpse. There, beetles have carved a swath through the shady oak groves that used to grow in canopies over campgrounds and picnic areas. Crews have removed nearly 1,000 trees at a cost of $1,000 per tree, for a total expense of about $1 million, said Roger Covalt, supervising ranger for the park.

Although campers have complained about the loss of their favorite shade trees at William Heise County Park, Covalt said park officials had no choice. Dying oaks could topple and kill visitors, they increase fire risk and they form vectors for infestation of new trees, he said.

Park officials plan to turn some of the cleared spots into picnic areas, and they have built 11 cabins on other cleared sites.

Birds and deer appreciate the fresh scrub that has cropped up where the oaks were cut, Covalt said, although some species dependent on the trees are losing habitat. Crews are replanting in some of the clearings, mostly with cedars and pines instead of oaks.

“Why plant (oaks)?” Covalt asked. “Then 15 years from now, if they haven’t found a solution to the gold-spotted oak borer problem, we’re looking at removing those.”

Mark Hoddle hopes to beat the beetle before then.

As director of the Center for Invasive Species Research at UC Riverside, Hoddle has trekked through the oak borer’s homeland to find its natural enemies.

The beetles don’t seem to pose a problem in Arizona, he said. Although they also inhabit oaks there, they rarely kill them.

Hoddle said Arizona oaks, which evolved with the oak borer, might be more resistant to them. In California, the beetles target specific trees in the red oak family: California live oak, black oak and canyon live oak. Other species aren’t affected, and those may be less susceptible to the beetle.

But Arizona forests may also be getting help from insects that keep oak borers in check. So Hoddle traveled to Arizona’s Sky Islands — isolated mountain ranges surrounded by desert — in a bid to discover where the oak borer originated.

He and other researchers narrowed their territory to the Dragoon Mountains, where they found parasitic wasps that devour the oak borer’s eggs and larvae. They’re testing the wasp species in a climate-controlled biosecurity lab.

It could take several years before scientists know if the wasps can effectively kill the oak borers — and do so without harming beneficial insects, Hoddle said.

“At this stage, I think that biological control is the best option we have for controlling this pest,” he said. “We can’t spray our oak forests. They’re just too big (and) the sprays would cause too much collateral damage.”

Meanwhile, Ostrander and about 280 other volunteers continue to scout their communities for oak borers, educate neighbors about the problem and warn against transporting firewood.

Edwina Scott, executive director of the Mountain Communities Fire Safe Council in Idyllwild, said volunteers there are mobilizing to stem the oak-borer outbreak. The beetle has killed seven trees in the town.

“We’re hoping to learn from what has happened in San Diego and reduce the effects of the oak borer before it spreads,” Scott said.

Citing the significance of oak groves in history and contemporary recreation, Jacumba volunteer Ostrander said people owe it to future generations to save the trees.

“Citizen scientists are going to be very important, because they are, for lack of a better word, foot soldiers going out in their communities and saying this is going on and if we take action, we can stop it,” Ostrander said. “I just really believe that what we do now is going to be our legacy to our children and grandchildren.”